The present invention relates to an electroded ceramic metal halide lamp (CMH) assembly, and more particularly, to the lumen maintenance of a CMH.
CMH lamps can have severe degradation in 100 hr lumens. Such degradation has been known to occur quickly, for example, reduction of 100 hr lumens by 25% in the first 1000 hours of lamp operation. Degradation is believed to arise from wall blackening of the arc-tube.
Lumen degradation is primarily due to the transport of tungsten to the walls of the discharge tube, by sputtering during starting, and by chemical transport as halides of tungsten in steady state operation. While halides are necessary components of the arc discharge fill, the transport of tungsten during steady state operation is greatly enhanced by the formation of excess halides, such as iodine. Excess iodine found in most high-intensity discharge (HID) lamps is bound by mercury, which forms a mercury iodide.
In order to optimize lumen maintenance, a design choice is sometimes made that shifts the lamp into a design space that sub-optimizes other key critical-to-quality (CTQ) factors such as color rendering index (CRI), correlated color temperature (CCT), color control, etc. However, it would be desirable to reduce the impact of lumen degradation without sacrificing other CTQ factors.